CENOZOIC GEOLOGICAL PROCESSES AND THEIR BEARING ON HYDROCARBON MIGRATION AND ACCUMULATION IN THE CONTINENTAL MARGINAL BASIN GROUP OF THE NORTHERN SOUTH CHINA SEA

The northern continental marginal basin group of the Southern China Sea, which includes the Yinggehai Basin, the Beibuwan Basin, the Qiongdongnan Basin, the Pearl River Mouth Basin and the Taixi'nan Basin, are located in a very complex geological setting. The formation and evolution of these basins are closely related to the surrounding geological processes. This paper reconstructed the paleo-geographical framework of some key time boundaries since 55 Ma, based on which simply discussion was paid to the migration and accumulation of oil and gas in the area. Following conclusions are reached. (1) The interaction among the Pacific Plate, the Eurasia Plate and the India-Australia Plate affects the formation, migration and accumulation of hydrocarbon in this area. (2) Source rocks are gradually getting younger, as the source rocks and the Mohos are getting deeper from west to east in the Pearl River Mouth Basin, Qiongdongnan Basin and Yinggehai Basin. At the same time, heat flows as well as the potentials of hydrocarbon generation increased. Similar trend of mantle depths are observed in the Beibuwan Basin, the Pearl River Mouth Basin and the Qiongdongnan Basin from north to south. (3) Oil and gas are enriched in the Yinggehai Basin, Qiongdongnan Basin and southern Perl River Mouth Basin while the geological activities are weak, the subsidence is small and the crust is thin (the Moho depths are less than 24km) so that the geothermal gradients and the heat flows are high in this region. Such conditions can keep the organic matters remained mature or over-mature, which are favorable for the formation of gas source rocks. (4) The hydrocarbon in the Qiongdongnan Basin and the Pearl River Mouth Basin is more prospective than that in the other basins. Especially, the Qiongdongnan Basin and the southern Pearl River Mouth Basin are likely to be the important gas producing area while the northern Pearl River Mouth Basin bears higher oil producing potential.